This invention relates in general to a replenisher mechanism for a developer station of a reproduction apparatus, and more particularly to an electrographic reproduction apparatus development station where the replenisher mechanism for resupplying of marking particle material to a reproduction apparatus development station provides highly accurate and continuous monitoring of the amount of marking particle material remaining in the housing of the replenisher mechanism so as to determine when and how much marking particle material to add to the replenisher mechanism.
In typical commercial reproduction apparatus (electrographic copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged charge-retentive or photoconductive member having dielectric characteristics (hereinafter referred to as the dielectric support member). Pigmented marking particles are attracted to the latent image charge pattern to develop such image on the dielectric support member. A receiver member, such as a sheet of paper, transparency or other medium, is then brought into contact with the dielectric support member, and an electric field applied to transfer the marking particle developed image to the receiver member from the dielectric support member. After transfer, the receiver member bearing the transferred image is transported away from the dielectric support member, and the image is fixed (fused) to the receiver member by heat and pressure to form a permanent reproduction thereon.
The pigmented marking particle material in such apparatus is typically contained in a replenisher housing and metered out to a development mechanism by a delivery mechanism as needed. Marking particle material, added to the replinisher housing from a receptacle such as a bottle or box, is typically a dry powder with particle size less than 20 microns. It is generally quite cohesive and as a result does not flow very well. Due to these characteristics of the marking particle material, it is very difficult to provide a device that can accurately and continuously monitor the amount of marking particle material remaining in the replenisher housing. Devices that can sense the presence or absence of marking particle material exist and are typically used to indicate when the level in the replenisher housing drops to specific discrete levels such as when it is nearly empty. In this case the amount of marking particle material remaining in the replenisher housing is known only at the discrete instant in time when the sensor changes state and the accuracy is limited by the physical size of the sensor and the uncertainty due to any meniscus effect. One can attempt to continuously monitor the amount of marking particle material remaining in the replenisher housing by monitoring the elapsed time of running of the delivery mechanism combined with a predetermined amount of marking particle material delivered by the delivery mechanism per unit of time. However due to the above mentioned poor flow property of typical marking particle material, the delivery rate has a level of uncertainty also.
Some manufacturers of these types of reproduction apparatus have attempted to determine, on a continuous basis, the amount of marking particle material in the replenisher housing based on some knowledge of the amount of material consumed per output print. In an optical light lens reproduction apparatus, an average material takeout per print might be assumed. Obviously any deviation from average will result in inaccuracy in the computed amount of material remaining in the replenisher housing. In a digital reproduction apparatus a material takeout per print might be calculated based on the number and level of pixels being printed. Any error in the assumed marking particle material delivery to the pixels impacts the accuracy of this material computation method.
In a production printing application, it is highly desirable to be able to run a reproduction apparatus continuously for long job runs without having to stop to add marking particle material to the replenishment housing. This requires that the reproduction apparatus operator receive an accurate indication of the amount of marking particle material remaining in the replenisher housing at any time, especially before starting a long job.
In view of the above, it is the object of the present invention to provide a replenisher mechanism for a reproduction apparatus, which provides highly accurate and continuous monitoring of the amount of marking particle material remaining in the housing of the replenisher mechanism by a combination of discrete level sensors and continuous sensing of the delivery assembly elapsed activation time. The replenisher mechanism includes a housing having a plurality of discrete sensors for sensing the level of marking particle material within the housing. A delivery assembly provides flow communication of marking particle material between the housing and a remote developer station. A delivery assembly sensor senses the amount of marking particle material delivered by the delivery assembly. A logic and control unit is operatively connected to the housing level sensor and the delivery assembly sensor and, by using signals from both of these sensors, continuously and accurately determines the amount of marking particle material remaining in the housing so as to indicate when, and how much, marking particle material to add to the housing.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.